How to determine the geom type of each layer of a ggplot2 object?
ggplot2, ggproto, layer, proto, r
Solution
ggplot 2.2 update: If what you want is a character string naming the geom type, you can use:
sapply(p$layers, function(x) class(x$geom)[1])
which yields the first class name for the geom object of each layer. In the OP's example:
[1] "GeomRibbon" "GeomLine"
The code in the answers above no longer give the results shown for version 2.2 The accepted answer yields two NULL values, and the other answer yields full `ggproto` objects.
Problem
As part of an effort to remove a specific geom from a plot I've already created (SO link here), I'd like to dynamically determine the geom type of each layer of a ggplot2 object. Assuming I don't know the order in which I added layers, is there a way to dynamically find layers with a specific geom? If I print out the layers like I do below I can see that the layers are stored in a list, but I can't seem to access the geom type. ``` library(ggplot2) dat <- data.frame(x=1:3, y=1:3, ymin=0:2, ymax=2:4) p <- ggplot(dat, aes(x=x, y=y)) + geom_ribbon(aes(ymin=ymin, ymax=ymax), alpha=0.3) + geom_line() p$layers [[1]] mapping: ymin = ymin, ymax = ymax geom_ribbon: na.rm = FALSE, alpha = 0.3 stat_identity: position_identity: (width = NULL, height = NULL) [[2]] geom_line: stat_identity: position_identity: (width = NULL, height = NULL) ``` I'm not familiar with proto objects and things I've tried from the proto documentation don't seem to work (e.g. `p$layers[[1]]$str()`). Thanks to the answers below I was able to come up with a function that removes a layer dynamically: ``` remove_geom <- function(ggplot2_object, geom_type) { layers <- lapply(ggplot2_object$layers, function(x) if(x$geom$objname == geom_type) NULL else x) layers <- layers[!sapply(layers, is.null)] ggplot2_object$layers <- layers ggplot2_object } ```